(a) Technical Field of the Invention
The present invention generally relates to prism sheets, and more particularly to a prism sheet of a LCD's backlight module providing both latitudinal and longitudinal convergence and optimal horizontal and vertical viewing angles for the LCD display.
(b) Description of the Prior Art
A typical liquid crystal display (LCD) device usually installs a number of diffusion films and prism sheets between the LCD's panel and a light guide plate, so that lights emitted from the light guide plate is scattered by the diffusion film and then converged by the prism sheet toward the LCD panel, thereby, increasing the brightness of LCD panel in a range of viewing angles.
As illustrated in FIG. 1, a conventional prism sheet mainly contains a base layer 1 and a prism layer 2 formed on a side of the base layer 1. The prism layer 2 contains a plurality of parallel-arranged prism lenses 3 having a triangular cross section. Emitted lights from the light guide plate (not shown) is first scattered by the diffusion film (not shown) and then, due to the refraction effect provided by the prism lenses, converged toward a direction normal to the LCD panel (not shown).
In real-life applications, the convergence provided by the prism sheet could enhance the brightness of the LCD display. However, the viewing angle of the LCD display would also be limited by such convergence. Due to the structure of the conventional prism sheet, the range of viewing angles achieved usually could only satisfy either the vertical or the horizontal, but not both, viewing angles of the LCD display.
Accordingly, how to provide a prism sheet that could be mass-produced with the current industry expertise, preserve the benefit of enhancing LCD brightness, but achieve satisfactory viewing angles, both horizontal and vertical, required by the LCD display is the major motivation behind the present invention.